The presence of ice and snow on pavement such as roads, sidewalks, bridges, runways, and the like presents safety hazards and operational obstacles to many everyday activities such as driving, flying, etc.
Over the years, a variety of techniques have been used in the colder parts of the world to remove or destroy this ice and snow. The techniques utilized have ranged from simple mechanical approaches (e.g. shoveling or plowing) to heating (e.g. by means of buried heating elements or by the direct application of heat) to chemical methods (e.g. the use of de-icing chemicals such as sodium chloride and calcium chloride). Where large surface areas are involved, such as roadways and runways, a combination of mechanical de-icing (e.g. snowplowing) and chemical de-icing (e.g. salt mixed with sand) is commonly used.
The most commonly used chemical de-icer for highways is sodium chloride (or rock salt as it is sometimes called). Sodium chloride (i.e. salt) is used as a chemical de-icer because it is relatively inexpensive, it is readily available in large quantities, and it has an attractive weight efficiency as a de-icer. At the present time it is estimated that the USA, alone, uses about 9 or 10 million tons of salt each year for de-icing purposes.
From time to time, various suggestions have been made to use materials other than sodium chloride salt as a chemical de-icer for highways and other paved areas. However, the low cost of purchasing and applying sodium chloride salt as a roadway de-icer has tended to discourage commercial interest in alternative de-icers even though some alternatives have been proposed. For example, methanol and a mixture of calcium and magnesium acetates (commonly called "CMA") are both reported to be as effective as salt for roadway de-icing purposes. However, neither alternative has replaced salt as a highway de-icer.
In recent years, increased attention has been focused on the total economic impact of the use of sodium chloride salt as a highway de-icing chemical and it has been discovered that while the initial cost of sodium chloride salt is significantly lower than the initial cost of other chemical de-icers, the total cost of using sodium chloride salt as a highway de-icing chemical is enormous when consideration is given to the corrosive damage to vehicles and pavement, corrosiveness to metal structures such as bridge elements and highway reinforcing bars, and environmental damage to soil, water, plants and animals. By way of illustration, the U.S. Environmental Protection Agency published data in 1976 suggesting that the conservative cost of the damage resulting from the use of sodium chloride salt for highway de-icing is approximately fourteen times the direct cost of purchasing and applying the salt in the first instance. Against this background, the State of South Dakota has already limited future use of sodium chloride salt for highway de-icing purposes and other political bodies may take similar actions in the future.
With these economic incentives, new research interest has been directed toward the idea of developing alternative de-icing chemicals that would have a total cost (e.g. on a state wide basis) which would be significantly less than the total cost associated with the use of sodium chloride salt as a highway de-icer. However, if the highway community is to be provided with an effective, non-corrosive, environmentally acceptable chemical de-icer, it is necessary to develop commercially attractive production methods. Processes must be found that are economically attractive and produce the de-icing product at an acceptable cost. To reduce transportation costs, it would be desirable if the de-icing product could be made from raw materials that are found in the geographic areas that use de-icing chemicals.
Against this background, there has been renewed interest in the possible use of a generally equi-molar mixture of calcium and magnesium acetates (commonly referred to as "CMA") which has shown considerable promise as a de-icing chemical. Limited field tests have confirmed its ability to function as a de-icer. Moreover, CMA does not contain the chloride ion which is present in sodium chloride salt and which is responsible for many of the corrosive side-effects of using sodium chloride as a highway de-icer. However, CMA is expensive to manufacture if it is prepared by classical chemical methods using relatively pure chemicals. Consequently, some suggestions have been made that a less pure form of acetic acid might be used in an effort to reduce the cost of making CMA and some consideration has been given to the possibility of producing CMA by a process in which a crude form of acetic acid is made by reacting cellulose with alkali metal or alkaline earth metal hydroxides at atmospheric pressure. For example, it is known that acetic acid can be made by fusing sodium hydroxide with cellulosic materials to provide yields of acetic acid of about 15 percent. However, it has been noted that the production of acetic acid by this route is accompanied by the production of large amounts of oxalic acid. Since the salts of oxalic acid are potentially dangerous to the environment, acetic acid must either be made by a different mechanism or the oxalic acid must be separated from the acetic acid before CMA is prepared and used as a roadway de-icer. Research continues toward this end.
Under the circumstances, there exists a continuing need to develop practical, alternative chemical de-icers which will have a significantly lower economic and environmental consequences.